1. Field of the Invention
This invention relates to location determination of one or more wireless devices.
2. Prior Art
Location determination technology—the ability to identify the location of electronic devices—has evolved toward more accurate location determination. The evolution of this technology has been driven by the need to solve several important problems, such as the location of emergency service workers (emergency rescue/fire personnel), the location of people who are in danger (such as users of E-911 cellular service), and accurate indoor location determination.
Unfortunately, large steel and concrete buildings, subways and large malls may be difficult or even impossible to cover using traditional wide area location technologies, because low signal-to-noise ratio and signal multipath effects in these environments often decrease tracking accuracy or even prevent signal acquisition.
Multiple story buildings pose additional obstacles for tracking, as they require three-dimensional positioning. Even if the longitude and latitude of an individual in a fifty-story building were known with great accuracy, that knowledge would be insufficient because the emergency team may have to search every floor. For an accuracy of 200 meters, the location fix may cover many multi-story buildings. Under these conditions, a rescue team could spend hours just searching for the caller.
Present techniques for locating electronic devices (e.g., cellular phone, PDA or computer, etc.) in both indoor and outdoor environments (such as shopping malls, urban canyons, or office buildings) require either: 1) satellite (global positioning signals “GPS”) signals; or 2) GPS and assistance via cellular signals to penetrate building structures, when required; or 3) triangulation using the cellular system, or 4) some use of broadcast and/or RF signaling, or 5) some combination of these techniques.
Presently, two major approaches to GPS precision location dominate. The first, a mostly outdoor location fix technology, is the satellite vehicle-based Global Positioning System that receives a feeble code division multiple access “CDMA-like” signal from several satellites in which a receiver (using complex search routines and hardware) determines its position via the delay calculated using the received GPS signal phase, the GPS almanac and ephermis. This procedure takes several minutes in weak signal environments. The second is a system that extends the above system through use of additional information supplied via a cellular wireless network.
Snaptrack has disclosed a ‘communication’ system for providing GPS aiding information useful in the above second system (e.g., see U.S. Pat. Nos. 5,841,396 and 5,874,914). Communication systems require two-way signaling and information transfer. The concept is known as Assisted GPS. The SnapTrack implementation uses a communication system to send the GPS almanac, ephermis, and transfer of time from the base station to the mobile. In one mode, intermediate results are returned to the base station (and network) for further processing. With these quantities (GPS hints), the correlating receiver knows what and when to look for the appropriate satellites and can add the successive correlations of several tens of measurements, effectively pulling the feeble buried signal out of the thermal noise.
MeshNetworks has disclosed a method for location determination based upon range measurements between the portable device to be located and several fixed reference stations (see U.S. Pat. Nos. 6,768,730 and 6,728,545). This invention uses these range measurements to solve simultaneous (spherical) equations to obtain a 3-dimensional location. The accuracy of this approach is suspect, due to the fact the RF transmission is performed at (relatively) low power and is not reliable at great distances or indoor environments.
Hall, et al., has disclosed a Method and apparatus for geolocating a wireless communications device whereby the time difference of arrival for a signal received at two or more receiving sites as transmitted from a wireless communications device, is determined by a frequency domain technique. To determine the mobile location based on the determined time difference of arrival values, a seed or initial location is first assumed for the wireless communications device and the distance difference of arrival (the time difference of arrival multiplied by the speed of light) is calculated. The calculated time difference of arrival is then used to adjust the distance difference of arrival by continuously iterating the position of the wireless communications device until the calculated distance of arrival and the calculated time difference of arrival (as multiplied by the speed of light) are within a predetermined margin.
Many location determination inventions (too numerous to explicitly reference herein) have been disclosed based on Time Difference of Arrival, Time of Arrival, Enhanced-Observed Time Difference of Arrival (E-OTD), Angle of Arrival (obtaining multiple Lines-of-Bearing and solving for their intersection), and range measurements (solving for intersecting arcs or spheres). These are often combined or augmented with GPS technology. Most of these employ existing cellular infrastructure and/or other technologies which operate at frequencies too high for reliable penetration of indoor environments.
FM and other broadcast signals represent an improvement over higher frequency GPS/cellular RF signals in that they have been proven to penetrate the concrete, steal, and glass of the typical urban structure.
The Rosum Corporation has disclosed a method and apparatus for determining the position of a user terminal (e.g., see U.S. Pat. No. 6,859,173) by using a combination of broadcast signals and cellular radio signals. The method determines a first pseudo-range between the user terminal and the television signal transmitter based on a known component of the broadcast television signal; it determines a second pseudo-range between the user terminal and the mobile telephone base station based on a known component of the mobile telephone signal; and it determines a position of the user terminal based on the first and second pseudo-ranges, a location of the television signal transmitter, and a location of the mobile telephone base station; wherein the mobile telephone signal is selected from the group consisting of a EDGE (Enhanced Data Rates for Global System for Mobile Communications (GSM) Evolution) signal; a Code-Division Multiple Access 2000 (cdma2000) signal; and a Wideband Code-Division Multiple Access (WCDMA) signal.
Trimble has disclosed an invention addressing the location of emergency service workers (e.g., see U.S. Pat. No. 5,552,772) whereby they use a wide array of location determination methods, one of which is a set of unsynchronized FM sub-carrier signals to perform range measurements or TDOA measurements. To obtain TDOA measurements from unsynchronized signals, the invention specifies the existence of an independent “observer module” that observes the difference in synchronization between the various reference stations and informs the receiver of the differences. The receiver then uses the synchronization difference values, combined with TDOA measurements, to derive its location.
Trimble has disclosed a portable hybrid location determination system describing an apparatus and method for determining the present location of a mobile user that carries the apparatus inside or outside buildings and structures within a region R. The apparatus includes a radio location determination (LD) signal module that receives radiowaves from at least three radio LD signal sources, such as FM carrier or subcarrier signals, and an outdoor LD signal module that receives outdoor LD signals from at least three other satellite-based or ground-based outdoor LD signal sources, such as GPS, GLONASS or Loran-C signal sources. The radio LD signals and outdoor LD signals are used to (1) determine the location of the radio LD module, (2) determine the location of the outdoor LD module and (3) determine an indicium representing signal strength or signal quality for the radio LD signals and for the outdoor LD signals. The radio LD signal indicium and the outdoor LD signal indicium are compared with threshold values for these indicia, and at most one of the radio LD module location and the outdoor LD module location is selected as the present location of the apparatus user. The radio LD module and the outdoor LD module can be combined in a hybrid portable LD system, or the two modules can be separated from and move independently of each other.
Texas Instruments has disclosed an invention addressing the location of cellular telephones (and other potential applications) by the use of broadcast signals, such as AM, FM, non-DTV, etc. (see U.S. Pat. No. 6,806,830). In this disclosure, both synchronized and unsynchronized broadcast signals are used. For unsynchronized signals, TI also uses an independent “observer module” to measure the deviation from synchronization. A drawback is that the solution may not provide sufficient geographic dispersion of the broadcast stations to obtain reliably accurate fixes. Further, this solution will not provide reliably accurate 3-d fixes because the probable location of the transmission stations does not provide the necessary angular geometry to accurately measure elevation.
There continues to exist a need in the art for a method and apparatus for location determination of people or object that addresses the problems cited above, such as poor indoor location performance, RF signal degradation, and the introduction of errors due to weak signal or multipath. Specifically, it would be desirable to have an method and apparatus that performs reliable and accurate 3-dimensional location determination for both indoor and outdoor locations. Such a method and apparatus may be used in cellular telephone networks (in support of E-911 or other location-based services), by emergency first responders (fire, rescue, police, swat, etc.), or for any other location determination application.